Some pieces of agricultural equipment known in the art as forage harvesters and combine harvesters are used to collect and process crop material from a field. Generally, such agricultural harvesting machines are equipped with crop material cutting and/or collecting devices, such as maize, corn or grain cutting headers or pick-up units for picking up e.g. hay, grass or straw off the ground. In addition to such initial gathering operations, the machines are also provided with second-stage gathering means for transferring crop material and include intake elements for taking in harvested/gathered crop material and feeding it to further crop processing means of the harvesting machine.
In a forage harvester, for example, the intake elements usually comprise a set of feedrolls which take in harvested crop material and feed it to a cutterhead, which is part of the further crop processing means. The rotating cutterhead co-operates with a fixed shear bar, operable to chop up the crop material fed thereto by the feedrolls. With grasslike materials, which are kernel-free, it is sufficient to comminute the crop material, e. g. the stems of the plants are cut to length using a cutterhead such as a rotary knife drum. When cutting maize, the cobs may be comminuted into smaller size segments by the cutterhead, and it is preferred that the majority of the kernels are broken or cracked, which is needed in order to facilitate the complete digestion of the crop material, including the maize kernels, by the farm animals. Therefore a compressor roll assembly, comprising a set of closely adjacent, co-operating compressor rolls with fluted surfaces, may be provided for cracking the chopped crop material. The comminuted/processed crop material is then propelled by a blower or accelerator out of the harvester through a spout, directing the material flow into a temporary container travelled behind or aside the forage harvester, before being stored and eventually being foddered to livestock.
In a combine harvester, for example, the intake elements generally comprise a straw elevator, which feeds the crop material to the crop processing means comprising threshing means, including one or more threshing drums, further separation means, such as straw walkers, and cleaning means, including sieves and a ventilator, operable to remove impurities such as chaff and pieces of straw from the grain kernels.
In use, in order to harvest crop material, an agricultural harvesting machine is provided at its front with a header that is adapted for cutting and gathering crop material and feeding the crop material to the feedrolls, and the feedrolls are adapted to feed the gathered crop material to the further processing means. The header therein typically comprises transfer means for transferring the gathered crop material to an intake mouth of the harvesting machine, formed by the feedrolls, the intake mouth generally being of a smaller width than the header.
The length to which the crop material is cut depends on the conveyance speed of the feedrolls and on the speed of the processing means such as the cutterhead.
With a forage harvester, when crop material is fed to the feedrolls at too high a speed (speed of the header transfer means being higher than the speed of the feedrolls), a plug of material is formed in front of the feedrolls, which hampers the crop flow and causes material to be unevenly cut. If the speed of the header is lower than the speed of the feedrolls, material may be grasped by the feedrolls and torn apart. Furthermore, in such cases, an irregular length of cut is obtained at the cutterhead, while in both cases a stationary length of cut is desired. Also when picking up e.g. hay, grass or straw, problems can be caused due to the speed of the header transfer means compared to the speed of the feedrolls: if the speed of the header is too low, material will pass below it and will be lost; if the speed of the header is too high, hay will be pushed forward. Here again, an irregular length of cut will be obtained.